The invention relates to etching a substrate in a process zone.
In the manufacture of integrated circuits, active and passive devices are formed on a substrate, such as a semiconductor wafer, by alternately depositing and etching layers of dielectric, semiconducting, and conducting materials, such as silicon dioxide, polysilicon, and metal-containing materials. These layers may be etched to form a pattern of etched features in a predefined pattern of gates, vias, contact holes, trenches, and/or metal interconnect lines. Etching is typically performed using an energized etchant gas, such as a halogen-containing gas, as for example described in Silicon Processing for the VLSI Era, Vol. 1, Chapter 16, by Wolf and Tauber, Lattice Press, 1986, which is incorporated herein by reference.
The predefined pattern may be formed by providing photoresist over an underlying material to be etched. The photoresist may be patterned by lithography to expose portions of the underlying material. However, when photoresist is used it often is difficult to maintain the critical dimensions of the etched features. It is also difficult to obtain good etching selectivity for etching underlying material relative to the photoresist, especially when the underlying material is an oxide. In addition, while etching the underlying material, process conditions are generally selected to preserve the photoresist to prevent premature removal of the photoresist and also to reduce deposition of process residues on chamber or substrate surfaces. Furthermore, residual photoresist portions that are not etched by the etchant gases and which remain on the substrate after the etching process may need to be removed in a post processing step. Conventional photoresist removal processes, also known as stripping or ashing, are sometimes ineffective in removing all the resist from the substrate without overexposing a processed substrate to the energized stripping gas. In addition, resist removal processes compromise process throughput by adding a process step and a separate process chamber.
The process chambers used in processing a substrate are periodically cleaned to remove process residue deposits and contaminants that are formed on the surfaces in the chamber, otherwise these deposits may flake off and contaminate the substrate. In etching processes, after etching every 100 to 300 wafers, the chamber is often opened to the atmosphere and cleaned in a “wet-cleaning” process, in which an operator uses an acid or solvent to scrub off or dissolve accumulated etch residue on the chamber surfaces. After cleaning, the chamber is pumped down in a vacuum for 2 to 3 hours to outgas volatile species, and a series of etching runs are performed on dummy wafers until the chamber provides consistent etching properties. However, the downtime of the etching chamber during the cleaning process can substantially increase the cost per substrate. Also, because the wet cleaning process is manually performed, the cleanliness of the chamber surfaces often vary from one cleaning session to another.
Therefore, it is desirable to be able to etch a substrate with improved critical dimension control and etching selectivity. It is further desirable to process the substrate with increased throughput. It is still further desirable to process a substrate in a substantially clean process chamber to reduce the possibility of contaminating the substrate. It is still further desirable to remove sufficient amounts of etch resistant material from the substrate without undesirably etching the substrate with the energized gas.